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<a name="Conversions"></a>
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<a name="Conversions-1"></a>
<h3 class="section">14.13 Conversions</h3>
<a name="index-conversions"></a>
<a name="index-machine-mode-conversions"></a>

<p>All conversions between machine modes must be represented by
explicit conversion operations.  For example, an expression
which is the sum of a byte and a full word cannot be written as
<code>(plus:SI (reg:QI 34) (reg:SI 80))</code> because the <code>plus</code>
operation requires two operands of the same machine mode.
Therefore, the byte-sized operand is enclosed in a conversion
operation, as in
</p>
<div class="smallexample">
<pre class="smallexample">(plus:SI (sign_extend:SI (reg:QI 34)) (reg:SI 80))
</pre></div>

<p>The conversion operation is not a mere placeholder, because there
may be more than one way of converting from a given starting mode
to the desired final mode.  The conversion operation code says how
to do it.
</p>
<p>For all conversion operations, <var>x</var> must not be <code>VOIDmode</code>
because the mode in which to do the conversion would not be known.
The conversion must either be done at compile-time or <var>x</var>
must be placed into a register.
</p>
<dl compact="compact">
<dd><a name="index-sign_005fextend"></a>
</dd>
<dt><code>(sign_extend:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of sign-extending the value <var>x</var>
to machine mode <var>m</var>.  <var>m</var> must be a fixed-point mode
and <var>x</var> a fixed-point value of a mode narrower than <var>m</var>.
</p>
<a name="index-zero_005fextend"></a>
</dd>
<dt><code>(zero_extend:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of zero-extending the value <var>x</var>
to machine mode <var>m</var>.  <var>m</var> must be a fixed-point mode
and <var>x</var> a fixed-point value of a mode narrower than <var>m</var>.
</p>
<a name="index-float_005fextend"></a>
</dd>
<dt><code>(float_extend:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of extending the value <var>x</var>
to machine mode <var>m</var>.  <var>m</var> must be a floating point mode
and <var>x</var> a floating point value of a mode narrower than <var>m</var>.
</p>
<a name="index-truncate"></a>
</dd>
<dt><code>(truncate:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of truncating the value <var>x</var>
to machine mode <var>m</var>.  <var>m</var> must be a fixed-point mode
and <var>x</var> a fixed-point value of a mode wider than <var>m</var>.
</p>
<a name="index-ss_005ftruncate"></a>
</dd>
<dt><code>(ss_truncate:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of truncating the value <var>x</var>
to machine mode <var>m</var>, using signed saturation in the case of
overflow.  Both <var>m</var> and the mode of <var>x</var> must be fixed-point
modes.
</p>
<a name="index-us_005ftruncate"></a>
</dd>
<dt><code>(us_truncate:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of truncating the value <var>x</var>
to machine mode <var>m</var>, using unsigned saturation in the case of
overflow.  Both <var>m</var> and the mode of <var>x</var> must be fixed-point
modes.
</p>
<a name="index-float_005ftruncate"></a>
</dd>
<dt><code>(float_truncate:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of truncating the value <var>x</var>
to machine mode <var>m</var>.  <var>m</var> must be a floating point mode
and <var>x</var> a floating point value of a mode wider than <var>m</var>.
</p>
<a name="index-float"></a>
</dd>
<dt><code>(float:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of converting fixed point value <var>x</var>,
regarded as signed, to floating point mode <var>m</var>.
</p>
<a name="index-unsigned_005ffloat"></a>
</dd>
<dt><code>(unsigned_float:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of converting fixed point value <var>x</var>,
regarded as unsigned, to floating point mode <var>m</var>.
</p>
<a name="index-fix"></a>
</dd>
<dt><code>(fix:<var>m</var> <var>x</var>)</code></dt>
<dd><p>When <var>m</var> is a floating-point mode, represents the result of
converting floating point value <var>x</var> (valid for mode <var>m</var>) to an
integer, still represented in floating point mode <var>m</var>, by rounding
towards zero.
</p>
<p>When <var>m</var> is a fixed-point mode, represents the result of
converting floating point value <var>x</var> to mode <var>m</var>, regarded as
signed.  How rounding is done is not specified, so this operation may
be used validly in compiling C code only for integer-valued operands.
</p>
<a name="index-unsigned_005ffix"></a>
</dd>
<dt><code>(unsigned_fix:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of converting floating point value <var>x</var> to
fixed point mode <var>m</var>, regarded as unsigned.  How rounding is done
is not specified.
</p>
<a name="index-fract_005fconvert"></a>
</dd>
<dt><code>(fract_convert:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of converting fixed-point value <var>x</var> to
fixed-point mode <var>m</var>, signed integer value <var>x</var> to
fixed-point mode <var>m</var>, floating-point value <var>x</var> to
fixed-point mode <var>m</var>, fixed-point value <var>x</var> to integer mode <var>m</var>
regarded as signed, or fixed-point value <var>x</var> to floating-point mode <var>m</var>.
When overflows or underflows happen, the results are undefined.
</p>
<a name="index-sat_005ffract"></a>
</dd>
<dt><code>(sat_fract:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of converting fixed-point value <var>x</var> to
fixed-point mode <var>m</var>, signed integer value <var>x</var> to
fixed-point mode <var>m</var>, or floating-point value <var>x</var> to
fixed-point mode <var>m</var>.
When overflows or underflows happen, the results are saturated to the
maximum or the minimum.
</p>
<a name="index-unsigned_005ffract_005fconvert"></a>
</dd>
<dt><code>(unsigned_fract_convert:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of converting fixed-point value <var>x</var> to
integer mode <var>m</var> regarded as unsigned, or unsigned integer value <var>x</var> to
fixed-point mode <var>m</var>.
When overflows or underflows happen, the results are undefined.
</p>
<a name="index-unsigned_005fsat_005ffract"></a>
</dd>
<dt><code>(unsigned_sat_fract:<var>m</var> <var>x</var>)</code></dt>
<dd><p>Represents the result of converting unsigned integer value <var>x</var> to
fixed-point mode <var>m</var>.
When overflows or underflows happen, the results are saturated to the
maximum or the minimum.
</p></dd>
</dl>

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